Our research on Pavlovian aversive (Av) to instrumental appetitive (Ap) transfer has shown that a danger signal (AvCS plus) contingent upon the food-reinforced response in a visual choice discrimination facilitates learning whereas a safety signal (AvCS minus) retards learning. These and other findings suggested that a CS functioned to signal the presence (CS plus) or absence (CS minus) of one type of affective event (e.g., Av) and that such a function readily transferred to a qualitatively different (Ap) reinforcer. Subsequent investigations of the mediational properties of the CSs indicated, however, that our findings were better interpreted as across-reinforcement blocking effects: A response-contingent AvCS minus or CS plus, by signaling a preferred or a non-preferred outcome (absence or presence of shock), produced little if any or a large positive discrepancy with the preferred outcome of food reinforcement and thereby blocked or counterblocked (enhanced) the association of reinforcement and the SD. This blocking interpretation has been supported by recent studies investigating (1) Ap to Ap transfer in the same discrimination-learning paradigm and (2) Ap to Av transfer in a conditioned-suppression paradigm. Our future research will investigate factors controlling these within and across-reinforcement blocking effects and the specific interpretations which may account for them. Assessment will be made of (1) qualitative and quantitative variations in the reinforcers (Ap or Av) employed, (2) the kinds of learning processes that are affected, i.e., conditioning-extinction and excitatory-inhibitory processes, and (3) the nature of the compounds, e.g., simultaneous or sequential, used to generate blocking effects in both Pavlovian and instrumental/operant tasks. The latter will include investigation of response-reinforcer relationships where, in the absence of discriminative control, the instrumental response may itself be blocked or counterblocked by a contingent CS.